1. Field of the invention
The invention relates to a method for determining a composite material constitutive of moving parts, such as crankshafts, connecting rods, pistons and valves, of a hermetically sealed refrigerating compressor and a refrigerating compressor comprising such parts made of composite material whose determination has been performed through using the present method.
2. Summary of the prior art
For many years efforts have been made to reduce the mass or weight of moving parts found in refrigerating compressors or units, especially the crankshafts, connecting rods, pistons and valves, since these parts consume a considerable amount of energy with respect to the total amount of energy required for the compression of the refrigerating fluid.
Furthermore, in compressors that comprise an uneven number of pistons, it is necessary to add balancing counter-weights in order to reduce the forces of inertia. These counter-weights have masses that proportionally reduce the efficiency of the compressor.
The reduction of the moving masses leads to a reduction in the power necessary for the motor, thus of the size of the windings and furthermore a reduction of vibrations and noise.
In numerous industrial applications, use is made of composite materials, i.e. synthetic materials mixed with fibrous materials, in order to produce structures having a reduced mass or weight with respect to the former known solutions.
It has thus been envisaged to utilize composite materials during the production of the moving parts of compressors.
However, if in certain applications the use of composite materials raises no particular problem, the same is not true for the production of hermetically sealed refrigerating compressor parts.
Indeed, in the other fields, the choice of materials is most often made in function of their mechanical or thermic properties. Thus, for example, during the production of body parts for a land vehicle, it is of great importance that the various elements be capable of withstanding mechanical stresses to which they are submitted. For the obtention of thermal insulating elements or of elements which contact heated parts, it is of great importance that the elements be capable of withstanding the thermal stresses.
For the production of parts which are intended to be moved inside compressors, the composite material has to be determined as a function of the particular and simultaneous conditions of use.
On the one hand, the moving parts are subjected to high mechanical stresses; on the other hand, the operating temperature is high, in the region of 200.degree. C.; furthermore, the environment in which these elements are located is chemically very corrosive.
The mechanical and physical properties are determined for several temperatures, but in non-corrosive environments. Furthermore, the manufacturers determine the chemical stability of a given composite material in a given environment for several temperatures but without mechanical stresses. Therefore, the only knowledge of propertles given by a manufacturer does not allow to determine in advance whether a material is suitable or not for producing the above-mentioned compressor parts.
The invention is based upon these observations and relates to a method for determining a composite material intended to be utilized in the production of parts moving in a hermetically sealed refrigerating compressor, and a hermetically sealed refrigerating compressor comprising the parts determined by this method.